[ATSF3751]

Here is an interesting subject someone started on a Facebook page. Thought I would pass this along and see what you guys all thought.

The throttle on a steam locomotive can be barely open but the locomotive can act like it is wide open

The throttle limits the flow of steam from the boiler through the piping to the valves. The more the throttle is open, the greater flow of steam is allowed to pass through. When the throttle is barely open, a small flow of steam is allowed through the throttle to the valves. The throttle does not limit the pressure of the steam but the flow.

If a locomotive is running and the throttle is barely open, the movement of the pistons use up the steam as it is being admitted and the pressure is not allowed to build up to a high pressure. However when the locomotive is sitting still and the throttle is barely open, steam is not being use and the system is a closed/contained pressure vessel. The steam will pass through the throttle and pressure will build up in the cylinders until the drivers rotate or until the pressure in the cylinders is equal to the boiler; at that point the pistons will have the maximum force on them from the full boiler pressure even though the throttle is barely open.

If the throttle is opened when the brakes are applied to load up the cylinders with steam before releasing the brakes to move or the throttle is left open to build up pressure as the locomotive slowly starts to move, the pistons can be subject to a good amount of steam pressure and this can cause the drivers to slip. Kinetic friction (friction between spinning wheels and the rail) is less than static friction (wheels holding the rails) so once the wheels break loose, they will spin easily until the steam pressure acting on the piston drops quite a bit and the power drops quite a bit.

This is why many engineers pump the throttle (opening and closing the throttle) when starting; this gives only bites of steam to the cylinders to meter the amount of steam and not allow the pressure to keep climbing.

Hope you find this interesting and also a little helpful to make Open Rails even more realistic when it comes to steam.

Brandon

[copperpen]

I think that the operation of steam locomotives in Open Rails is extremely close to realistic already. The throttle works almost as you describe. The bit missing from the description is the steam chest where the steam from the boiler is stored before admission to the cylinders. Then we have the reverser/Johnson bar which controls the actual amount of steam that is admitted to each cylinder per stroke. If this is in mid gear there will be no steam moving from the steam chest to the cylinder. This is how it should be set with brakes applied if the engine is to stand for any length of time. This is how Open Rails steam works.

[darwins]

Are twin port regulators currently supported?

If they are what is the correct way to write them into the engine controllers section?

(To date I have been copying MSTS entries without knowing if they are either functional or correct.)

[copperpen]

Far as I know, and I may be wrong, only a simple single port throttle is coded. Having a twin port would be useful as it would then be possible to have finer control over the start in inclement weather and slow speed control.